Neutralized vacuum-tube circuits



Jan. 20, 1931. R. K. POTTER 1,789,416

NEUTRALIZED VACUUM TUBE CIRCUITS Filed NOV. 3. 1927 Osc.

I N VEN TOR.

REPoLer BY W ATTORNEY Patented Jan. 20, 1931.

Zf N- TE STATES 3? 31m n K. POTTER, on N W YORK-,VN; Y., Assienon o AMERICAN TELnPiioiv E A vnf TELEGRAPH coMraivm-a CORPQRATION-DFNEWYORK 7 u' mealt mes; vAoiiiI'ivi-ri BE oiaciiirs Applifeation filed November 3, 1927. i Serial No. I 230,910.

This invention relates 'tovacuum tube cirfcuits'and more particularly to vacuum tube circuitshaving a feed-back connection from the output to the input-for instances, oscil- 5-lator circuitsof certain typesand regenerative circuits. 7

Y The problem solved by the applicant will be better understood from the following discussion relating to oscillator circuits 5' In the -10 generation of short radio waves it has been v found advantageous to make use of'socalled controlled oscillatorsthat is, oscillators in which the frequency is stabilized'byimpressing upon the grid, for instance, a wave of the desired frequency from a constant source. When the natural frequency of the controlled oscillator diiiers slightly froin that of the controlling wave from the associated source, the reaction in anunneutralized cir- V cuit arrangement tends to produce a change in the frequency of the stabilizing source; For a given vacuum tube oscillationcircuit the current fed back through the capacity 1 from plate to grid increases with the fre- 4 quency. Accordingly, it will readily be understoOd-that the'reaction due to the feeding back of energy comes to have a particular im- I portance in the generati'onof shortj'radio' waves. Furthermore, there are, of course,

a many-cases in which it is desirable to impress upon the grid of a vacuum tube oscillator waves quite different in frequency from the natural period of the oscillator; In the absence of neutralization there will be a tend- --ency for the modulated oscillator toreact upon the associated circuit, changing the frequency if the frequency separation is small,

or modulating back upon -the-plates of the associated vacuum tube apparatus. 4 Y The object of this invention is to prevent the above-discussed reaction'upon the associated modulation circuit due to the feed ing back of energy in the oscillatorcor similar feed-back circuit.

I 4 'This object the'applicant accomplishes by balancingthe inter-electrode impedances of the oscillator circuit and so arranging the circuits that in the element of the oscillator through Which the coupling to the associated circuit is-eflected the feed-back currents are :neutralized'and' so have no effect on thec as scription. It is proposed to s'how in some detail the application of the invention to three -controlled oscillator arrangements differing somewhat and to a regenerative'radio receiving circuit. The principles 'ofthe invention 7 which underlie the arrangements 'of these" illustrative circuits Will be clarifiedfby a schematic disclosure of the inter-relation of I type-herein considered.

Accordingly, Figure l of impedances-ina vacuum tube circuit of [the the accompanying drawing-showsschematically the imped ance relations involved in'the' arrangements disclosed in the other figuresof the'drawing. Fig. 2 shows diagrammaticallyja simple c0" n trolled oscillator circuit neutralized in accordance with the invention. Fig. 3 shows a -controlled"osci'llator. of the pushfpullftype similarly neutralized Fig. 4'sh'o'ws a circuit far'rangement comb ning a neutralized oscil- "lator and a inodulation circuit (the term modulation circuit? being used in its .IHOIG Jgenerally acceptedse'nse) Fig: shows diagrammatically a simple regenerative radio receiving circuit neutralized in accordance with the invention. i 1

"With reference, first, to Fig.1 of thedrawing, the inductances and the capacity of the oscillatory circuitare represented by L and C respectively. In accordance with conven tion, the plate outputof the vacuum tube which generates the oscillations is represented by"'a small generator e connected in series'with the filament-plateresistance of the vacuum tube (R,,). The filan ient'plate capacity C 3, is connected in parallel with the generator and the filament-plate resistance, and both elements are bridged across a part or" the oscillatory circuit inductance L. It is assumed'that the grid oi thevacuuintube generator is made sufliciently negative to prevent the flow of conductive current.

The I remaining I intebelectrode impedances may now be repi'esentedbythe capacities (1.; and C5,, the grid-filament and the grid-plate 1-mp edances, respectively. In accordance with ionv I the invention, the-balancing or neutralizing capacities 6' and C are added to the c1rproper selection of the neutralizing im pedance values -It will be understood, of

course, that the inductive "coupling here trolled oscillator circuits. )lator should be preferably a shielded vacuum shown is for the purpose of illustration." Other couplings, capacitive or through resistance, may be employed.

drawing, but bearing in mind the schematic disclosure of Fig. 1, the reader will under stand the practical application ofthe ideas of the invention. Fig.1 2 shows'an oscillator circuit arrangement havinga generator tube T. The battery B serves tobias the grid of the tube T, and the battery B provides the positive. potential which is maintained on the plate. The resonant vcircuit of the oscillator comprises the condenser C and the 001i winding W. Through this windingVV and the associated winding. W the oscillator circuit is coupled to the output circuit. The winding W in the grid circuit is associated with a winding W and byithis coupling means the stabilizing frequency fromthe controloscillator isimpressedupon the con- This control osciltube generator of the crystal controlled type or anordi nary oscillator: which is carefully shielded to preventany exposure except that through its balancedoutput. 1 It will be noted that the oscillatorcircuits are divided, and in particular thereisa connection to an intermediate point of the winding W The ca .pacities to balance the inter-electrode capacities are here'shown in the form of the con densers C C and C It is to be understood that these elements represent balancing impedances, which might. in accordance with the requirements of an individualcase, take the. form of a capacity with a resistance and an inductance added, or some other form of impedance to suit the case. Again, a dummy vacuum tube arrangement may be used "in a symmetricalcircuit to form the balancing impedance. What is essential is that impedances are added to balance the interelectrode impcdances so that the current flows through the two parts of the coil W5, will be equal in amplitude and opposite in phase.

InFig. 3 of the drawing there is shown the application of .the'invention to a well-known type of push-pull oscillator, including the tubes T and T associated, asshown, with a control oscillator which furnishes the stabihzing frequency. The resonant circuit is formed by the capacityCf and the inductance are" W, and the inter-electrode impedances of the tubes T and T are balancedby the auv.

iliary impe'dances (here shown as capacities) (1' (1' C and C CS, C' respectlvely.

The element of the oscillator circuit through which, this circuit isicoupled tothe control oscillator is, of course, divided as was the case is Fig. 2.. 'The winding WV is assocically in Fig. tofthedrawing, the control oscillator, the coupling to the controlledosthe coupling winding W ,ofthe outp'utcircuit and the balancing impedances 07 ,07

theplate battery'B of Fig. 2, however,the re is here substituted amodulator circuit 'as shown. -Here again the inter-electrode im-u pedances are balanced, and there isneutralization of the. feed-back current flow'in 'cillator circuit,-.the.tube T", the elements C andW forming the resonant circuit, Turning attention now to Fig.2 of the that portion of the oscillator circuit-which is coupled to the controloscillator, reaction upon the control oscillator being thus prevented; v

In Fig. ,5 of the drawing the invention is applied to a regenerativeradio receiving circuit. The vacuum tube TT has associated with 1t the usual grid and plate batteries.

The receiving antenna'circuit; including the antenna A and .thewinding WW, is c'ou- H pled to the vacuum tube circuit through the winding WW, which, with thevariable condenser Q0 forms a tuned circuit. The plate circuit lstuned toparallel resonance'hy 'adjustment of the resonant arrangement'includ- .lIlg the windin WVV and the Variable com denser CC. Thewinding WW is coupledto the winding W W .inthe grid circuit to feed energy back into that circuit in a manner well understood in the art. The coil W W also is coupled to the winding VVW' to form the output of the system; If, now, there are added the balancing impedances CC and CC there is a balance of the imp'eda'nces of in common and each WW". Accordingly, the feed-back currents in the two parts of the winding W will be equal in amplitude and opposite in phase, no voltage being induced in the winding WW". Thus, there is no reaction upon the input or modulation circuit due to thefeed back currentsof the vacuum tube circuit.

the two circuits having tlieI i g vvvvl a part ofthe. winding I15 While the invention has been disclosedfor the purpose of illustration in certain specific embodiments whichare deemed desirable, it is to beunderstood that such disclosure in no way limits the scope of the invention, which is defined in the appended claims. l/Vhat is claimed is;

'1. In a vacuum tube circuit having a feed back connection fromfthe output portion. to the input-o'portionthereof and a control cirfeed-back currents therelni cuit associated therewith, the method of pre-' Venting the feed-backof energy into the con; trol circuit, which consists'in balancing the inter-electrode 'impedances of the, vacuum tube circuit, and neutralizing the flow of fl ked-back currents in the input portion there- V x 2. In a vacuum tube circuit havinga feedsaid input circuit to neutralize the flow of I In testimony whereof, I haveisigned my name to this specification this 18th day of O tober, 1927;

back connection from the output portion to theinput portion thereof and a control cir cuit associated therewith, the method of preventing the feed-back of energy into the control circuit, which consists in dividing the vacuumtube circuit, and balancing the intralize the flow of feed-back currents in the v cuit, an output circuit, and a feed-back con-.

the control circuit, which consists in dividter-electrode impedan'ces thereof so as to neuing the vacuum tube circuit, balancing the inter-electrode impedances thereof, and neutralizing the effect of the feed-back currents 1 in the two parts of the input portion thereof.

4. In an electrical-system including a vacuum tube arrangement having an input c1r- 'V nection from said outputcircuit to said input circuit, a c1rcu1t associated with said 1n'-' put circuit for supplying a modulating potential thereto, auxiliary impedances for balancing the vacuum tube inter-electrode impedances, and means for neutralizing the flow of feed-back currents in the vacuum tube input circuit. 7 y I 5. In an electrical system including a vac"- uum tube arrangement havlng an input c1rcuit, an output circuit, and a' feedback connection from sald output c1rcu1t tosald lnput c1rcu1t, a c1rcu1t coupled to said input c1rcu1t for supplying a modulating potential there- 7 to, auxiliary impedances for balancing the vacuum tube inter-electrode impedances, and circuit connections whereby feed-back currents in the coupling element of the input circuit are neutralized.

6. In an electrical system, a vacuum tube" oscillator, a control oscillator associated with the input circuit'thereof, means for balancing the vacuum tube inter-electrode impedances,

and means for neutralizing the feed-back currents in the input circuit of the oscillator to prevent reaction of saidcurrents on the control oscillator.

7 In an electricalsystem, a vacuum tube 7 oscillator, a control oscillator coupled to the input circuit thereof,auxiliary impedances 1n the oscilator c1rcu1t for balancing the in- 

